JPH11216862A - Thermal ink-jet print head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a nucleus formation effect of a heating resistor by providing a base body having an array of the heating resistor on a surface and an address electrode formed on the array and including in the heating resistor a specific first layer and a specific second oxide layer on the first layer. SOLUTION: A heating resistor 20 is formed on a layer 19 and comprises two layers 20A, 20B. The layer 20A is formed of, e.g. zirconium diboride and sputtered to a depth of approximately 0.5 mm in the layer 19. The zirconium diboride forming the layer 20A is electrically conductive having a sheet resistance of 5-1,000 ohms/square and a surface roughness smaller than 0.5 nmRSM. The layer 20B is a thin film of, e.g. zirconium diboride oxide of a thickness 200 Å-1 μm. After the formation of the layer 20A, a small quantity of an oxygen flow is introduced into a pile of ZrB2 in a sputtering chamber, thereby forming the layer 20B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates generally to thermal ink jet printing, and more particularly to a printhead having a resistive heater with improved droplet ejection effects.

[0002]

2. Description of the Related Art In general, thermal ink-jet printing is a drop-on-demand type ink jet that uses heat energy to generate vapor bubbles in a channel filled with ink to discharge droplets. It is a print. The thermal energy generator, or heating element, is typically a resistor and is located in the channel near the nozzle and at a predetermined distance from the nozzle. The ink nucleation method first involves shorting individual resistors (2-6 μm).
Seconds) Addressing (designating) with an electric pulse and instantaneously vaporizing the ink to form a bubble that ejects ink droplets. As the bubbles grow, the ink bulges from the nozzles and is held as a meniscus by the surface tension of the ink. As the bubble begins to collapse, the ink still between the nozzles of the channel and the bubble moves toward the collapsing bubble, causing the volume of the ink to shrink at the nozzle, thereby separating the puffy ink as droplets I do. By accelerating the ink out of the nozzles while the bubbles are growing, the droplets can be given momentum and velocity in a substantially linear direction toward a recording medium such as paper.

A heating element during a droplet discharging operation is in an environment of high temperature, thermal stress, large electric field and remarkable cavitation stress. Therefore, it was early recognized that a cavitation stress protection layer was needed over the heating element. One very good material for this purpose is tantalum (Ta), as is well known in the art.

It has been demonstrated that the nucleation efficiency depends on the properties of the heater surface (Paper by Michael O'Horo et al., "Effect of TIJ heater surface topology on steam bubble nucleation", SPIE Journal, Vol. 2658. 58th-6th
4, p. 29 Jan. 1996). In this paper, experimental observations have shown that there are two types of vapor bubble nucleation, homogeneous nucleation and heterogeneous nucleation. Uniform nucleation occurs spontaneously in the ink when the nucleation temperature is reached. Heterogeneous nucleation usually occurs at the surface portion of the resistance heater (cracks and crevasse). The surface portion contains trapped gases and vapors, which make the onset temperature for heterogeneous nucleation much lower than that for homogeneous nucleation. The efficiency of the energy stored in the ink and the resulting expansion of the vapor bubbles is greatly reduced.

The prior art relating to controlling the surface roughness of ink jet heating elements to control vapor bubble nucleation includes:
There is U.S. Pat. No. 4,336,548, which describes techniques and materials used to manufacture thermal inkjet printheads with increased surface roughness. The surface roughness according to this patent is much greater than the roughness described herein and is utilized to enhance the degree of heterogeneous nucleation during the formation of a vapor bubble. This technique is accomplished by roughening the surface of the substrate layer by sandblasting, etching, or other techniques prior to deposition of the heating resistor material and passivation stack.
As a result of these techniques, vapor bubble nucleation actually occurs with low energy input, but due to the low degree of overheating of the ink, the energy of the ejected droplets is limited to the liquid generated by uniform vapor bubble nucleation. It is much smaller than a drop and therefore less effective. U.S. Pat. No. 4,336,548 claims the use of zirconium oxide as a heater passivation material, as well as hafnium and zirconium diboride, among other materials, as heating elements, similar to the present invention. On the other hand, US Pat.
Before the attachment of the heating resistor and the passivation stack,
Although patents describe the use of lasers or electron beams (among other techniques) to melt the substrate surface to create a relatively smooth surface, this patent includes metal diboride as a heater material. , Oxide as a passivation dielectric and tantalum as a protective layer. However, in both of these prior arts, diboride is used only as a heat energy generating layer (heating resistor), and variations of the heater surface finish include varying degrees of smoothing of the substrate. Only proposed. No effort has been made to alter the deposition of heater or passivation material to increase the smoothness of the final heater surface. Further, if there are heating element materials and passivating oxides, they are sequentially deposited in both of these patents using two different sputtering targets or other deposition sources. In contrast, in the present invention, the heater material layer and the oxide layer are deposited in-situ simply by changing the deposition conditions at the end of the deposition sequence, and the interface between manufacturability and heater / passivation. Can be significantly improved. The configuration described in the present invention is advantageous because the substrate (polished microelectronics type single crystal silicon wafer with thermally grown oxide) is already very smooth and requires no further processing. It has further advantages compared to. According to the technique described in the present invention, an already relatively smooth heater, fabricated on a smooth single crystal silicon substrate, deposits a particulate metal diboride heating element and cleans its surface layer. In-situ oxidation during the deposition of the heater material further smoothes it so that the roughness is below the nanometer scale (up to two grades larger than the heater described in US Pat. No. 5,287,622). Good) integrated heater / passivation stack.

[0006] The preferred material for the resistance heater is a sputtered thin film resistor material such as polysilicon or zirconium diboride (ZrB2). Polysilicon consists of a number of grains whose dimensions and roughness vary with deposition conditions, subsequent high temperature cycling, and doping levels. The surface roughness of the polysilicon of the high-dose injection heater (heater 2 described in O'Horo's article) is 27.2 n.
m. ZrB immediately after deposition obtainable by the present invention
The surface roughness of No. 2 is 0.5 nm. The resistive heater is then passivated using a thermally grown oxide layer or pyrolytic CVD deposited silicon nitride, both of which closely replicate the surface roughness of, for example, polysilicon to the surface of the passivation layer. Thus, the roughness is quite consistent. A tantalum layer is optionally sputtered over the passivation layer, which adds additional features and substantially mirrors the shape of the underlying layer so that the Ta grain structure is approximately 15 nm RMS or greater. Therefore, the surface of the tantalum layer replicates the surface side and is therefore of this type (conventional dielectric passivation layer and polysilicon or tantalum with tantalum).
The roughness and nucleation effects of the polysilicon below the heater structure of rB2) are not optimal.

From the above, it is clear that the smoother surface of the resistive heater surface enhances the nucleation effect by reducing the number of cracks or crevasses that trap the vapor. U.S. Pat. No. 5,469,200 discloses a method of polishing a substrate of a heating resistor to improve its flatness, and in another example, forming a thermal oxide by oxidizing the substrate surface simultaneously with a thermal softening step. As a result, a technique for obtaining a smoother surface on the oxide passivation layer is disclosed. These techniques are not entirely satisfactory because they are not compatible with integrated microelectronic circuits due to excessively high temperatures and / or long heating cycles. In addition, these techniques attempt to reduce the surface shape of the final heater surface by simply changing the shape of the initial substrate surface, reducing the shape provided by the resistive heating element and its passivation stack. And therefore,
The degree of smoothness that can be obtained is limited.

[0008]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a resistance heater having a smooth surface, thereby enhancing the nucleation effect of the resistance heater used in a thermal ink jet printhead. I do.

[0009]

SUMMARY OF THE INVENTION To this end, in a preferred embodiment, a resistive heater having a very smooth surface of zirconium diboride, a particulate thin film resistive material, is provided by a sputtering process. Form. The sputtering step involves introducing oxygen at a controlled rate towards the end of the formation of the first conductive layer. The introduction of oxygen forms a thin film on top of the underlying conductive layer. This film has a significantly increased sheet resistance and a very smooth surface (0.5 nm RM
(Smaller than S).

More particularly, the present invention comprises a substrate having on one surface an array of heating resistors and address electrodes formed thereon, wherein the heating resistors are of the general formula (A) B2
A first layer of a sputtered thin film resistor compound of
On the first layer is characterized by including a second oxide layer having the general formula (A) B2Ox, wherein B is boron, A is zirconium (Zr), molybdenum (M
o), one metal selected from the group consisting of hafnium (Hf), niobium (Nb), tantalum (Ta), titanium (Ti), vanadium (V), and tungsten (W). And a thermal inkjet printhead.

The present invention also provides an improved printhead for use in an ink jet printer having a plurality of ink-filled channels in thermal communication with at least one portion of a thermal resistor. Comprising: (a) sputtering a layer of a resistive material of general formula (A) B2 onto the surface of a substrate, and (b) introducing oxygen at the end of the sputtering step to form Forming an oxide layer having a relatively high sheet resistance and a surface roughness of less than 0.5 nm RMS, and (c) forming a plurality of ink filled ink channels in thermal communication with the thermal resistor.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the improved resistance heater structure.
It is sectional drawing which shows an Example. This resistance heater structure can be used, for example, in printheads of the type disclosed in U.S. Pat. Nos. Re. 32,572; 4,774,530 and 4,951,063. The contents of these patents are incorporated herein by reference. Obviously, other types of thermal inkjet printheads that heat the resistive element to nucleate the ink in adjacent layers can also use the improved heater structure of the present invention.

FIG. 1 shows a heater base portion of the ink jet print head 8 together with ink in a channel 10 discharged from a nozzle 12 formed on the front surface. The print head 8 is similar to the above-mentioned U.S. Pat.
No. 2,572 and U.S. Pat. No. 4,951,063 by a conventional method of joining the channel and the heating plate (except for the formation of a heating resistor). The silicon substrate 16 has an underlayer 18 formed on the surface. In one embodiment, it is a thermoformed field oxide. If the chip also has active circuitry, a gate oxide layer 19 is formed on the surface of layer 18. The gate oxide is an active MOS transistor elsewhere on the chip
Formed as a component of a transistor device, it merely serves in the heater structure to slightly increase the amount of oxide under the resistive heating element. Heating resistor 20 is formed on layer 19. In accordance with the present invention, and in the preferred embodiment, resistor 20 comprises two layers 20A, 20B, shown in greater detail in FIG. Layer 20A is
In a preferred embodiment, zirconium diboride,
Layer 19 is sputtered to a depth of about 0.5 mm. The zirconium diboride forming layer 20A is electrically conductive and has a sheet resistance of 5 to 1000o.
hms / square, surface roughness is 0.5nm RMS
Is less than. Layer 20B is a thin film of zirconium diboride from 200 Å to 1 micron,
Following formation of layer 20A, it is formed during the deposition of ZrB2 by introducing a small flow of oxygen into the sputtering chamber. By incorporating oxygen during film growth, the sheet resistance of zirconium diboride is significantly increased, resulting in a layer 20B having a sheet resistance in excess of 7000 ohms / square. More importantly, the membrane 20B keeps its underlying shape smooth and is significantly smoother than prior art polysilicon resistors. Although a silicon nitride or oxide layer may be used to form layer 20B, such a separately deposited film will have a very rough surface finish and a layer 2B.
It will reduce the benefits provided by the 0A ultra-smooth heating resistor material. Layer 20B is masked and etched with layer 20A to form a suitably sized heating resistor element. If desired, a tantalum layer 30 (FIG. 2) may be formed on layer 20B. However, this tantalum layer also significantly increases the final heater surface roughness, and depending on the deposition conditions, limits the final roughness obtained to the tantalum film roughness of about 12-15 nm RMS. Would. For electrode passivation, a glass film 34 is deposited and then masked and etched through the glass film 34 and the oxidized zirconium diboride layer 20B to form vias 23, 24 at the resistor edges. . Biases 23, 24 are used for subsequent interconnections of aluminum address electrode 25 and aluminum counter return electrode 26, respectively.

For devices requiring more than one metal interconnect layer elsewhere on the chip, one or more additional passivation glass layers 34 may be placed over the heater interconnect electrodes. A final ion diffusion resistant passivation layer 35 may be deposited and typically a plasma enhanced silicon nitride material. A thick film insulating layer 36 is deposited and patterned, and the ink distribution channel and nozzle structure 1
0 is formed. Layer 36 is a polyimide in the preferred embodiment.

FIG. 2 shows that the sputtered ZrB2
ZrB2Ox that forms an ultra-smooth surface 20 over the surface of
Layer 20B is shown. Other suitable materials for layer 20A are metal diborides selected from Groups 4A, 5B and 6B of the Periodic Table of Elements, ideally zirconium, niobium, tantalum, titanium, vanadium, tungsten, molybdenum. And hafnium. While the embodiments disclosed herein are preferred, various alternatives, modifications, variations, or improvements can be made by those skilled in the art based on the teachings. All such variations are within the scope of the following claims.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of an improved heating resistor according to the present invention.

FIG. 2 is a further enlarged sectional view showing the resistor of FIG. 1;

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kathy Jay. Burke United States 14625 New York Rochester Spire Road 135

Claims (3)

[Claims] 1. A thermal inkjet printhead comprising a substrate having an array of heating resistors formed on one surface of the substrate, wherein the heating resistors have a general formula (A)
A first layer of a conductive diboride of B2 and a second oxide layer of the general formula (A) B2Ox on the first layer, wherein B is boron. And A is a metal selected from the group consisting of zirconium, molybdenum, hafnium, niobium, tantalum, titanium, vanadium, and tungsten. 2. The thermal ink jet printhead according to claim 1, wherein A is zirconium. 3. The thermal ink jet printhead of claim 1, wherein said second layer has a surface roughness of less than 5 nm RMS.